Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $14.57   13.836%   $16.5859   $16.59   $16.60   $16.60  
  Purchase #2 $125.49   9.440%   $137.3363   $137.34   $137.35   $137.30  
  Purchase #3 $56.85   9.594%   $62.3042   $62.30   $62.30   $62.30  
  Purchase #4 $123.72   9.368%   $135.3101   $135.31   $135.30   $135.30  
  Purchase #5 $208.34   7.758%   $224.503   $224.50   $224.50   $224.50  
  Purchase #6 $234.31   3.870%   $243.3778   $243.38   $243.40   $243.40  
  Purchase #7 $113.58   3.819%   $117.9176   $117.92   $117.90   $117.90  
  7 purchase totals = $876.86       $937.3349   $937.34   $937.35   $937.30